The present invention relates to a method of checking emergency shutdown of an ion beam therapy system which, in particular, is operated with heavy ions.
Ion beam therapy systems are preferably used for the treatment of tumors. They have the advantage that when a target is irradiated, the major part of the energy of the ion beam is transferred to the target, while only a small amount of energy is transmitted to sound tissue. Therefore, a relatively high irradiation dose can be used to treat a patient. By contrast, X-rays transmit their energy to the same extent to the target and to sound tissue, so that, for health reasons in order to protect the patient, a high irradiation dose cannot be used.
U.S. Pat. No. 4,870,287, for example, discloses an ion beam therapy system in which proton beams are generated by a proton source, it being possible for its protons to be fed to various treatment or irradiation stations via an accelerator device. At each treatment station there is a rotating frame with a patient couch, so that the patient can be irradiated with the proton beam at different irradiation angles. While the patient is located physically at a fixed point within the rotating frame, the rotating frame rotates about the body of the patient in order to focus the irradiation beams at different irradiation angles onto the target, located at the isocenter of the rotating frame. The accelerator device comprises the combination of a linear accelerator (LINAC) and a synchrotron ring, as it is known.
In H. F. Weehuizen et al, CLOSED LOOP CONTROL OF A CYCLOTRON BEAM FOR PROTON THERAPY, KEK Proceedings 97-17, January 1998, a method of stabilizing the proton beam in proton beam therapy systems is proposed, the treatment beam being controlled actively in such a way that, at two measurement points spaced apart from each other in the longitudinal direction, it lies on the center line of the corresponding beam feed system. The first measurement point is located between a pair of deflection magnets and is formed by a multiwire ionization chamber. Depending on the current value, supplied by this multiwire ionization chamber, of the beam position with respect to the center of the beam path, the PI control of further deflection magnets, which are arranged upstream of the first-named pair of deflection magnets, is produced. The second measurement point is located shortly upstream of the isocenter and is formed by an ionization chamber subdivided into four quadrants. Depending on the current position value from this ionization chamber, again PI control signals are generated, but these are intended for the first-named deflection magnets. The intention of this control is to permit both angular stability with respect to the center line of the beam feed system and lateral positional stability of the proton beam.
When carrying out heavy ion irradiation, that is to say an irradiation using ions which are heavier than protons, large and heavy equipment is required, however, so that here there is the tendency to avoid the use of rotary frameworks and, instead, to move the patient or the patient couch. Corresponding therapy systems are described, for example, in E. Pedroni: Beam Delivery, Proc. 1st Int. Symposium on Hadrontherapy, Como, Italy, Oct. 18-21, 1993, page 434. These systems are accordingly eccentric systems.
Since, however, fundamentally isocentric systems are preferred by oncologists, a heavy ion beam therapy system has been proposed in which, although rotary frameworks are used at the treatment stations, the radii of the rotary frameworks can be reduced by the treatment beam fed to each rotary framework horizontally along its axis of rotation being guided, with the aid of suitable magnetic and optical arrangements, in such a way that it firstly runs away from the axis of rotation and subsequently crosses the axis of rotation again at the isocenter in order to irradiate a target. In order to irradiate the target, a raster scanner is provided, which comprises vertical deflection means and horizontal deflection means which each deflect the treatment beams at right angles to the beam axis, so that an area surrounding the target is scanned by the treatment beams. This system therefore substantially provides beam guidance in only one plane of the rotary framework.
The irradiation by means of the raster scanner is carried out with the aid of irradiation dose data, which are calculated by the control system of the ion beam therapy system automatically, depending on the patient to be irradiated or to be treated.
Since, in principle, high operational safety and operational stability with regard to the treatment beam are required of ion beam therapy systems, in the case of the heavy ion beam therapy system described previously, a monitoring device is provided to monitor the treatment beam supplied by the raster scanner. This monitoring device is arranged between the last deflection magnet of the aforementioned magnet arrangement and the isocenter, and may comprise ionization chambers for monitoring the particle flux and multiwire chambers for monitoring the beam position and the beam width.
During the operation of medical electron accelerators, various DIN standards have to be complied with for reasons of safety. These relate firstly to acceptance testing, that is to say checking the operational readiness, and secondly testing the constancy, that is to say checking the operational stability, of the system. For ion beam therapy systems, in particular for heavy ion beam therapy systems, such safety standards developed specifically for ion beam therapy systems are not yet known. However, in the case of ion beam therapy systems there is also the requirement for the greatest possible operational safety and operational stability.
The present invention is therefore based on the object of proposing a method of checking emergency shutdown of an ion beam therapy system, in order to improve the operational safety and operational stability, in particular as referred to emergency shutdown. At the same time, the intention is for the method to be suitable in particular for use with heavy ions.
According to the present invention, this object is achieved by a method having the features of claim 1. The dependent claims in each case define preferred and advantageous embodiments of the present invention.
According to the present invention, an ion beam therapy system is operated which has at least one ion source, an accelerator device and a beam guidance system, a check of emergency shutdown being carried out.
For this purpose, a check is carried out of manual and automatic emergency shutdown with automatic monitoring of all the safety-relevant device parameters and with a display of all the safety-relevant states on consoles of a technical therapy control room and a main control room for the entire system of an ion beam therapy installation.
This check of the serviceability of an interlock unit or emergency shutdown of an ion beam therapy system is of a very high relevance in terms of safety.
For example, all the safety-relevant device parameters have to be checked upon the triggering of an emergency shutdown of the system in the event of an interlock case or an interlock condition being present. Shutdown of the treatment beam can be carried out only when an interlock case has been detected. Therefore, all sources which can lead to an interlock case must be simulated individually in a test, and the triggering of the interlock, that is to say the generation by the interlock unit of the signals that lead to the emergency shutdown of the treatment unit, must be checked. During operation, the interlock unit preferably monitors the signals from the limit switches of the moving parts in the beam guidance, the states of the magnetic network devices of the raster scanner magnets, the ionization chambers with regard to the voltage supply, a data overflow in the data transmission, compliance with intensity limiting values and synchronism of the individual ionization chambers, the electronics of the beam position measuring device and the beam position itself, the high voltage and the gas flow to the individual detectors, a possible interlock via the sequence control computer, the position of the patient couch, a possible interruption of the immobilization of the patient (for example in the event of opening the mask at the irradiation station or in the event of movement of the patient), the functional readiness of all the computer programs and possible emergency shutdown or release of irradiation via the medical operating console of the therapy system, etc. If the interlock does not trigger when an interlock state is present, action must be taken in the therapy system and the fault must be rectified. In order to test consistency, this check should be carried out daily.
Likewise, the serviceability of the manual emergency shutdown via the medical operating console must be checked, since manual emergency shutdown must be ensured at any time.
Finally, a check on the displays of all the safety-relevant states on the individual consoles of the ion beam therapy system, in particular of the technical control rooms and of the main control room, is needed. The display of these safety-relevant states is used for rapid fault detection and fault rectification, and provide [sic] the operating personnel with information about the instantaneous state of the irradiation. These displays of the alarm conditions can be checked together with the above-described test of the interlock unit. In order to test consistency, this test should be carried out before each irradiation block and after any change to the monitoring system or to the programs.
In particular, it is proposed to check the calculated irradiation dose values for a number of measurement points on the phantom, conclusions being drawn as to the adequate accuracy of the calculation of the irradiation dose data if the mean deviation between the calculated and measured values of the irradiation dose for all the measurement points does not exceed a predefined first tolerance value and, for each individual measurement point, the deviation between the calculated and measured irradiation dose for this measurement point does not exceed a predefined second tolerance. In this case, the first tolerance value is xc2x15% and the second tolerance value is xc2x17%.
In order to check the correct transmission of the geometric structures at the treatment station and the planning parameters of an image-providing device belonging to the ion beam therapy system as far as the positioning means, a digital reconstruction of the phantom, in particular a radiographic reconstruction, can be calculated and is compared with a radiograph of the phantom which is produced, in order to detect any possible deviation.
The present invention permits a considerable improvement in the operational stability and operational safety of the ion beam therapy system and defines a testing plan with specific testing aspects, which can be carried out with the effect of acceptance testing and/or consistency testing of the ion beam therapy system. This relates in particular to the irradiation planning, in the course of which irradiation dose data in the ion beam therapy system are calculated automatically, depending on the patient to be irradiated or treated.